A present invention relates to an adapter for adapting a uniform contact grid of an electronic testing device for testing PCBs (printed circuit boards) to an irregular contact configuration of contact points on a PCB to be tested.
A "universal adapter" in accordance with EP-B1 26 824 has a base plate lying on a base grid of a testing device, which is provided with channels or bores which pass through it corresponding to a uniform contact grid of the testing device. At a distance above the base grid concerned, that is on a side of the base plate facing away from the base grid of the testing-device, there is an arrangement of two spaced-apart adapter plates, disposed or positioned by fixed spacing means. These adapter plates are identically provided with bores which are distributed corresponding to variably disposed connection points of a PCB to be tested. Needle-like test pins, which are resilient longitudinally, are inserted into these bores in the adapter plates. These test pins are able to pivot resiliently outwards, at least in their lower section, transverse to a lengthwise direction of the test pins, thus to offset any defects of alignment between the testpiece-specific bores and the grid of the testing device connected channels. With such an adapter made up of several plates, a manufacturer of PCBs must prepare at least the testpiece-specific adapter plates for each test series, in order to be able to assemble an adapter at all. Thus, rationalization for production of adapters is, to this extent, not possible.
As many thousands of connection points can be provided in complex PCBs, and a resilient test pin is needed for each connection point, costs for such an adapter rise markedly with increase in the number of contact points, since test pins that are resilient in the longitudinal direction require production costs that are not inconsiderable. In addition, such test pins have a minimum practical diameter that represents a natural limit for the possible density of the test pins.
In order to be able to use test pins that are rigid in the longitudinal direction and that thus are easy to manufacture to be particularly thin, an "active base grid" has been produced in which contacts of the base grid of a PCB testing device are resiliently supported essentially in the direction of the longitudinal axis of the test pins. This active base grid is applied onto the rigid, hard-wired base grid of the PCB testing device and serves, when rigid test pins are used, to provide sufficiently high contact pressure which is as uniform as possible at all test points contacted by the rigid test pins.
EP-A1-0 215 146 shows an adapter ("adapter 85") having an upper testpiece-specific bored adapter plate that lies on a PCB to be tested and rigid contourless test pins that pass through an additional elastic mat disposed at a distance below the PCB. The elastic mat is unbored and, because of the elasticity of material of the mat, prevents falling out of the test pins during handling with the adapter concerned, independently of the actual testing device. In this way, upon subsequent testing of identical PCBs, the labor costs of fitting the adapter with test pins, which costs are not inconsiderable, can be saved. Such adapter can be stored again until it is again used. Such adapter has the advantage that rigid, completely contourless test pins, which can be manufactured very cheaply, can be used, although fitting of the adapter becomes more complicated in that the test pins cannot simply "drop into" the adapter, but rather have to be pushed through the unbored elastic mat with a certain force. This adapter furthermore has an inner adapter plate, a grid of which, however, corresponds neither to the grid of the outer adapter plate or to the grid of the base plate. This therefore means that it is necessary to manufacture at least one further adapter plate with a bore pattern which differs from that of a first-mentioned adapter-plate, in addition to the testpiece-specific bored adapter plate.
There are further adapter-designs for which an entire series of bored adapter plates are disposed between a testpiece-specific bored adapter plate and a grid-hole plate of an adapter lying on a contact point grid of a testing device. Bore patterns of the series of adapter plates produce a gradual transition from the testpiece-specific bored adapter plate to the grid-hole plate and therefore vary in each case and thus require higher production costs and costs for materials when producing such adapters. In addition, fitting such adapters with test pins is particularly difficult.
The adapters described above were designed for one side testing of PCBs. Increasingly however PCBs that have connection points on both sides are being used, and they must be tested on both sides. Two successive one-side tests can be used, although breaks in current due to so-called "risers" then will not be detected, such risers moreover being particularly sensitive to breaks in current. PCB testing devices therefore have been developed which are able to effect simultaneous testing on both sides of PCBs. This then also leads to a need for adapters for such testing devices. Unfortunately, many adapters can be used for simultaneous double-sided testing only in exceptional cases, since if connection points on both sides of a PCB to be tested are unevenly distributed, with the sometimes several thousand test pins there will result substantial deformation or displacement of the test-piece. This can lead to additional (new) defects in the connection paths, or even to breakage of the PCB, particularly with ceramic boards. With one-sided testing of PCBs, uneven distribution or localized concentration of test-pins cannot lead to such a disadvantageous effect, as abutment on the opposite side of a testpiece can be by a stable plate of the actual testing device, and such plate takes up all irregular inputs of force into the PCB, substantially without deformation, and thereby supports the PCB to be tested in a largely undeformed state. With simultaneous, double-sided testing of PCBs, this however is not possible, since rigid abutment either is not present on a second side of a testpiece, or is the testpiece-specific bored adapter-plate of the other adapter, whereby this adapter plate cannot be made to be rigid at will, particularly as it is frequently produced from acrylic glass or similar material, in order to facilitate a manual fitting of the adapter.
The problem of possibly missing abutment and therefore of localized application of excessive force to a PCB during simultaneous, double-sided testing thereof is overcome by an adapter per EP-0 315 707 ("adapter 87") by introducing additional support means into such adapter at particularly loaded points, as separately sprung support-pins for example. With further increasing densities of connection surfaces of PCBs to be tested, occurring as part of the miniaturization of PCBs or wiring carriers, it is becoming more and more difficult to provide the space necessary for these support pins between the actual test pins. In addition, production and insertion of the support pins into an adapter results in substantial additional production costs.
There are adapter arrangements including resilient test pins (U.S. Pat. No. 3,654,585) or flexible elastic bits of wire (EP-184 619) disposed, with comparable function, parallel to each other in an essentially rigid or compressible solid body, that is, a "vertical PCB". However, the actual translation or adapting between irregularly or unevenly disposed testpiece-oriented contact points and the contacts of the testing device in a strictly grid-shaped arrangement is brought about by an additional "transition plate" which in accordance with standard PCB technology is provided with contact surfaces that are offset from each other, on both board surfaces, and with "risers" for connection of the contact surfaces. These adapter arrangements therefore require increased production costs simply due to the requirement for the transition or adapter plate.